Paos are, generally, rather strong pieces, especially in crowded positions. However, here the number
of material is very limited and it is hard to imagine how can be Black mated even on the edge of the board.
White king is "unfortunately" very far, thus after some thinking it turns out White will have to mate using
immobilised black piece as a hurdle on eighth rank.

There are two candidates. A promoted black pao seems to be better as only one unit is required
for its immobilisation - it can be black or white. But there is no way to give mate in 4 moves using black pao.
Then, the other choice is black bishop. But! You have to immobilise it by two black pieces...
or you can use some white that can be Circe-selfprotected against bishop capture.

Oh yes, it works! Black promotes to bishop, White sets his paos and captures with bp and bB - giving unbelievable
mate... and it is possible to execute this plan in two ways! As a result we obtain the exact echo position, including even
wK, after a totally asymmetrical play.

Just go through the solution and admire all the tricks that the author was able to incorporate into this miniature...
it contains much more than hundreds of heavier positions. I've seen already many fairy helpmates, but this one
is one of the most memorable even after years...